Standard molar entropy

About: Standard molar entropy is a research topic. Over the lifetime, 1586 publications have been published within this topic receiving 29886 citations.

Adsorption of hexavalent chromium on manganese nodule leached residue obtained from NH3-SO2 leaching.

Abstract: Adsorption of hexavalent chromium onto manganese nodule leached residues was investigated as a possible alternative to the conventional methods of its removal from aqueous synthetic solutions. Adsorption behavior was studied as a function of time, pH, temperature, and concentration of adsorbate and adsorbent in acetic acid–sodium acetate buffer medium. Cr (VI) removal was pH dependent and was found to be of a maximum at pH 3. The applicability of the Langmuir isotherm to the present system was tested. Increased adsorption capacity with increased temperature indicates that the adsorption reaction was endothermic in nature. Based on these studies, thermodynamic parameters such as Gibbs free energy change ( Δ G 0 ), standard enthalpy change ( Δ H 0 ), and standard entropy change ( Δ S 0 ) were calculated.

Synthesis and characterization of a starch–AlOOH–FeS2 nanocomposite for the adsorption of congo red dye from aqueous solution

Abstract: This work described the synthesis and characterization of a starch–AlOOH–FeS2 nanocomposite for the adsorption of congo red (CR) dye from aqueous solution. The morphology of the starch–AlOOH–FeS2 was characterized by using scanning and transmission electron microscopy, N2 adsorption–desorption isotherms, X-ray photoelectron spectroscopy, and fourier transform-infrared spectroscopy. The adsorption of CR onto starch–AlOOH–FeS2 was evaluated as a function of contact time, solution pH, concentration and temperature. The adsorption results demonstrate that the maximum removal of CR was found to be at pH 5. The adsorption kinetics data fitted well to the pseudo first-order equation whereas the Freundlich equation exhibits better correlation to the experimental data. Thermodynamic parameters, such as the standard free energy change (ΔG°), the standard entropy change (ΔS°) and the standard enthalpy change (ΔH°), were also evaluated. The results suggested that starch–AlOOH–FeS2 is a potential adsorbent for CR dye removal from aqueous solution.

The heat capacity of MgCr2O4, FeCr2O4, and Cr2O3 at low temperatures and derived thermodynamic properties

Abstract: The heat capacity of synthetic eskolaite, Cr2O3, and of the synthetic spinels magnesiochromite, MgCr2O4, and chromite, FeCr2O4 were measured from 1.5 K to 340 K. For MgCr2O4, a substantial magnetic contribution to the entropy is revealed by a sharp peak in the heat capacity curve at 12.55 ± 0.05 K, which indicates the transition to antiferromagnetic long-range order. Integration of the heat capacity curve yields a value of 118.3 ± 1.2 J/(mol·K) for the standard entropy at 298.15 K, which is in excellent agreement with that calculated from phase equilibria studies on the reaction MgCr2O4 + SiO2 = Cr2O3 + MgSiO3. The new calorimetric results for Cr2O3 indicate a standard entropy at 298.15 K of 82.8 ± 0.8 J/(mol·K). The measurements for FeCr2O4 show three distinct heat capacity anomalies, one of which (peaking at 36.5 ± 0.2 K) was missed by previous low temperature heat capacity measurements, which only extend down to 53 K. Integration of the heat capacity curve yields a value for the standard entropy at 298.15 K of 152.2 ± 3.0 J/(mol·K) for FeCr2O4, some 6 J/ (mol·K) greater than the previous calorimetric value. These low-temperature heat capacity data were combined with high-temperature heat content measurements from the literature to derive heat capacity equations for all three phases to 1800 K. The resulting heat capacity equations were then used to extract revised recommended values of the standard enthalpies of formation and entropies of MgCr2O4 and Cr2O3 from phase equilibrium data. For FeCr2O4, the phase equilibrium data are of dubious accuracy, the enthalpy of formation is only approximate.